1. Field
The present disclosure relates generally to filtering and, in particular, to nonlinear filtering in digital signal processing. Still more particularly, the present disclosure relates to an apparatus, system, and method for implementing a nonlinear filter system for digital signal processing using polyphase filter banks.
2. Background
Digital signal processing (DSP) software and hardware is widely used in various systems. Typically, an analog signal is received through a channel and then sent into an analog to digital converter (ADC). The analog to digital converter converts the input signal into a digital signal. The digital signal is then processed using digital signal processing software, hardware, or a combination of the two.
An ideal system may be a linear system in which every portion of the path of the input signal from the source of the input signal to the input end of the analog to digital converter is substantially linear. Linear filtering may be used to correct for any linear distortion, adaptively cancel out noise, channelize the input signal, or some combination thereof. However, complex systems may not be linear. In other words, nonlinearity may be introduced along the path of the input signal. This nonlinearity may be caused by, for example, without limitation, the type of electronic hardware being used, the channel medium used to carry the input signal, bandwidth limitations in the analog to digital converter, quantization errors in the analog to digital converter, or some combination thereof.
Having a filtering system capable of reducing undesired nonlinear effects to improve system performance may be desirable. In particular, it may be desirable to have a filtering technique capable of analyzing an input signal, synthesizing an output signal, or both in a manner that reduces undesired nonlinear effects. However, some conventional techniques may be unable to reduce undesired nonlinear effects with a desired level of accuracy. Because models of nonlinear behavior are often expressed as higher order polynomials, designing filters based on these models may be more difficult and complex than desired.
Although some nonlinear filtering techniques are currently available, these filtering techniques may be unable to achieve high order harmonic interference separation from the signals of interest in nonlinear systems. Further, these filtering techniques may be unable to achieve the level of performance needed for use in transmultiplexing or subband coding. As used herein, transmultiplexing is the conversion of time multiplexed components of a signal to a frequency multiplexed version and back. Subband coding is the decomposition of a signal into different frequency components and the subsequent encoding of those frequency components. Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues.